Cold rolled silicon steel strip



Patented Jan. 20, 1942 2,270,762 COLD ROLLED SILICON STEEL STRIP WestonMorrill, Pittsfield, Mass., assignor to General Electric Company, acorporation of New York No Drawing. Application January 31, 1939, SerialNo. 253,804

" stabilizing anneal at about 850 C. in hydrogen,

9 Claims.

The present invention relates to cold rolled silicon steel strip andmore particularly to cold rolling silicon steel strip at temperaturesfar below those heretofore employed in the production of such material.Processes heretofore employed in cold rolling silicon steel strip areset forth in the patent to Smith No. 1,915,766, June 27, 1933, and inthe patent to Goss No. 1,965,559, July 3, 1934. While the Smith processusually employs only one cold reduction the process generally employedin the production of cold rolled strip for use in transformer cores isthat disclosed in the Goss patent and comprises two cold rolling stepswith intermediate normalizing at about 925 C. for a few minutes and,after the final cold reduction, a normalizing treatment at about 1100 C.in hydrogen for about four minutes.

It is one of the objects of the present invention to increase thepermeability and reduce the total Watt losses in cold rolled siliconsteel strip.

In a process such as disclosed in the Goss patent, the first coldrolling reduces the silicon steel from about .080 inch to .030 inch andthe second or final cold rolling effects a reduction from .030 inch to.011 inch. Although the rolling operation is generally designated coldrolling the temperature of the material during rolling is generallyabout 80 C. and in many cases well above 100 C.

.I have found that if the cold rolling of silicon steel strip is carriedout at lower temperatures, for example by maintaining the temperature of,the steel within the range of 20 C. to 30 C.

during the rolling operation, a considerable improvement is obtainedboth in the permeability and total watt losses of the steel. Thefollowing table shows the results of permeability tests on silicon steelstrip containing 2.96% silicon which was given two cold reductions attemperatures of --30 (2., 0., 100 C. and 200 C., with intermediate andfinal normalizing treatments as set forth above:

when the steel strip was thereafter given a the following results wereobtained:

- Maximum Rolling temperature permeability 18, 640 0 C 18, 640 100 C 16,620 200 C 12, 980

' terial rolled at 100 C.

Still further improvement in the magnetic properties of the cold rolledsteel may be obtained if the steel after being normalized as usual inhydrogen at about 1100 C. is normalized for a few minutes at about 800C. in a strongly oxidizing atmosphere or is annealed for a few hours atabout 850 C. in a mildly oxidizing atmosphere. The effectof these heattreatments is to stabilize the steel by reducing some of the carboninthe steel thereby eliminatin the possibilityof ageing. While theimprovement in magnetic properties obtained by the re-normalizingtreatment or subsequent anneal at 850 C. is particularly efiective insilicon steel which has been rolled at temperatures between 20 C. and

30 C., this heat treatment is also effective in reducing the watt lossesin any cold rolled silicon steel irrespective of the particulartemperature employed in the cold rolling.

When more than one cold rolling step is employed the final cold rollingtemperature appears to be more important than the temperature employedin the first cold rolling operation. The following table shows theeffect on watt losses at cycles and 10,000 B, and 15,000 B. obtainedwith 3% silicon steel strip cold rolled in two steps at temperatures ofC. Likewise the table shows the effect of two cold reductions at 0 C.and the effect of a first reduction at 80 C. and a second reduction at 0C. In each case the first cold reduction was from .080 to .030 inch andthe second cold reduction from .030 to .012 inch. In each case the stripwas normalized at 925 C. for live minutes in a hydrogen atmos- Rollingsilicon phere after the first cold reduction and was normalized at 1100C. for three minutes in a hydrogen atmosphere after the second coldreduction.

Watt losses First Second rolling tolling Where a cold reduction of thesilicon steel strip is efiected in one operation, as in Smith patent,theternperature for the cold reduction should be in the range of 20 C.to 30 C. for best resuits. Likewise, ,it two or more cold reductions areemployed, as in Goss patent, it is essential that a temperature in therange of 20 C. to 30 C. be employed in the second or final cold rollingoperation in order to obtain the best magnetic characteristics in thesteel strip.

I In addition to the improvement in permeability and watt losses whichmay be obtained by rolling silicon steel strip at very low temperatures,I have also found that silicon steel strip containing about 3% siliconrolls easier at 0 C. than the same material rolled at temperatures of 300., 100 C., 200C. or 460 C. This latter result is of course contrary towhat would be expected.

. What I claim as new and desire to secure by Letters Patent of theUnited States, is:

1. In cold rolling silicon steel strip, the step which comprisesmaintaining the temperature 4. In cold rolling silicon which compriseeffecting successive reductions of approximately 60 to 70% in the steel,the temperature of the steel being maintained within the range of C. toC. during the final reduction.

5. In cold rolling silicon steel strip, the steps which compriseeffecting successive reductions of approximately to in the steel, thetemrolling operation.

of the steel within the range of 20 C. to 30 C.

during the rolling operation.

2. In cold rolling silicon steel strip, the step which comprisesmaintaining the temperature of the steel strip about 0 C. during therolling operation.

3. In cold rolling silicon steel strip containing about 3% silicon, thesteps which comprise effecting successive reductions of approximately 60to 70% in the steel, the temperature of the steel being maintainedwithin the range of 20 C. to 30 C. during each of said reductions.

7. In cold rolling silicon steel strip, the steps which comprise rollingthe steel at a temperature within the range of 20 C. to 30 C.,normalizing the steel at about 1100 C. in a reducing atmosphere andthereafter heat treating the steel to reduce some of the carbon in thesteel, the temperature of the steel being maintained within the saidrangewluring the rolling operation.

8. In cold rolling silicon steel strip, the steps which comprise rollingthe steel at a temperature within the range of 20 C. to 30 C.,normalizing the steel at about 1100 C. in a reducing atmosphere andrenormalizing the steel for a few minutes at about 800 C. in a stronglyoxidizing atmosphere, the temperature of the steel being maintainedwithin the said range during the rollmaintained within the said rangeduring the rolling operation.

WESTON MORRILL.

steel strip, the steps

